The present invention relates to a resolution filter for a spectrum analyzer.
During a spectrum analysis, a predetermined frequency range is swept with a resolution filter that has a predetermined band width, which is why the resolution filter is also referred to as a sweep filter. One resolution filter for a spectrum analyzer with an analog construction is described for instance in U.S. Pat. No. 5,736,845. With resolution filters which have a conventional analog construction, it is possible to achieve only a limited sweeping speed, referred to as the K-factor, which determines and limits how fast the sweeping is conducted in conventional resolution filters.
It has been generally assumed up until now that sweeping can be conducted within Tres with an order of magnitude of 1/Bres=Tres so that the resolution filter would be still able to respond. This statement has been taught as a fact, similar to the time law in information technology. In any case, this statement is correct only if it is based on the principle of a fixed filter for all sweeping speeds.
Therefore, there is a need for a resolution filter that makes it possible to achieve an optimal resolution with a high sweeping speed.
These and other needs are addressed by a resolution filter that has either a complex pulse response hused(t)=C1xc2x7exe2x88x92C2xc2x7t2xc2x7exe2x88x92jxc2x7C3xc2x7t2 or a real pulse response hused(t)=C4xc2x7exe2x88x92C5xc2x7t2, in which C1, C2, C3, C4 and C5 are constants. Accordingly, sweeping can be conducted even with an infinite speed with an optimal complex resolution filter, without causing by this occurrences of amplitude and band width errors.
It has been further also shown that, although sweeping cannot be conducted with an unlimited speed in case of a real resolution filter, it is still possible to achieve a minimum K-factor of Kmin=0.88. Definition of the K factor: sweeping is conducted within Tres with 1/Kxc2x7Bres.
Still other aspects, features, and advantages of the present invention are readily apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the present invention. The present invention is also capable of other and different embodiments, and its several details can be modified in various obvious respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.